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In Reply to: RE: Sansui SP-3005 project confusion posted by Bill Fitzmaurice on October 05, 2016 at 07:52:49
I tried to input the same parameters into different software. The Sansui port appears to be tuned to 64Hz according to online calculators. I got around 70 using the helmholtz resonance formula, but that isn't really accurate. The big peak in the bass is present on every simulation I try.
When I measured the parameters of the driver, I used the me the methods in David Weems books, and the Elliot sound website. I used a signal generator, power amplifier, 10 ohm resistor, and radio shack DMM as a volt meter and frequency counter. I used the added mass method for calculating the Vas, I blu tacked a couple capacitors to the cone and then weighed them using my ortofon tracking force digital scale. I think I followed the method properly, but it's always possible I made a mistake since it's the first time I have measured a driver in over 20 years, and I am only a hobbiest.
That said if I did it all properly, the original enclosures do look like they have a big peak in the bass region. I don't want to build speakers with this characteristic, it won't sound any good. I never heard them before taking them apart so can't comment on original sound quality.
These speakers are from 1972, so definitely in the late 60s early 70s range.
For the rebuild, the consensus is to abandon the port and slightly increase enclosure size? I sure like how the response looks better when I simulate that version.
Follow Ups:
> These speakers are from 1972, so definitely in the late 60s early 70s range.
They would not have used T/S specs in the design stage. T/S was pretty much unknown outside of Australia/New Zealand until 1971, and it took a few more years before cabs using them appeared. The use of such a large diameter port relative to the driver size is also a giveaway that it was a seat of the pants design. Too bad, sealed it probably would have sounded pretty good.
This is a good point, I think my DMM is pretty close, (claims to be true RMS over a broader range than I am testing) but will redo tests with a VTVM to confirm.
What I think is screwing up the results a bit more is my amplifier, it has a fairly high source resistance.
Possibly your dmm does not measure voltages at varying frequency in a linear fashion, I had (have) the same issue recently using the 10ohm series resistor method. Fs le and re can be made but as for the remainder of t/s parameters its a crap shoot without a good bench meter...JH
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